1. Field
The following relates to retro-directive targets and communications using such retro-directive targets. More particularly, the following relates to retro-directive targets that have wide angles of acceptance and that are useful for carrying out bidirectional free-space optical communications.
2. Related Art
A retro-reflector or other retro-reflective device provides an impetus for carrying out bidirectional free-space optical communications. Such a device makes possible the ability to retro-reflect back to a point of origin a received transmission of electromagnetic energy, such as a light or “laser” beam. When combined with a modulator and demodulator, the combination provides the ability to carry on bidirectional free-space optical communications.
For instance, the demodulator may demodulate information that was modulated onto the laser beam at the point of origin by a source device; the retro-reflective device may retro-reflect the laser beam onto the modulator to form a retro-reflected beam for delivery back to the point of origin, and the modulator may modulate additional or different information onto the a retro-reflected beam as such retro-reflected beam is reflected back to the point of origin. A receiver at the point of origin, in turn, may receive the retro-reflected beam and demodulate the information carried therein. Accordingly, the source and the combination of the demodulator, modulator and retro-reflective device can exchange information.
Given that frequencies used to carry out such optical communications allow for an extremely fast exchange of information, this type of device is conducive to mass exploitation in not only commercial applications, such as high speed voice and data communications, but also in military applications, such as friend-or-foe identification and/or establishing a secure communication channel in battlefield conditions.
Hindering this exploitation, however, are (1) the ability of the retro-reflective device to passively reflect light in the direction of (i.e., retro-reflect back to) the source over a wide acceptance angle; (2) the ability to arbitrarily modulate the reflected light either in phase, amplitude and/or polarization without detrimentally limiting the acceptance angle of the retro-reflective device; (3) the ability to be powered by a low-voltage, small current power pack, such as a battery or fuel cell; (4) the ability to be formed into small form factor; and (5) the ability to be conducive to manufacturing processes, which in turn, leads to potentially low-cost and high-volume manufacturing processes.